Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 µm, or 1/100 the size of a cloud droplet on which water vapor condenses.
Water requires a non-gaseous surface to make the transition from a vapor to a liquid; this process is called condensation.
In the atmosphere of Earth, this surface presents itself as tiny solid or liquid particles called CCNs.
When no CCNs are present, water vapor can be supercooled at about −13 °C (9 °F) for 5–6 hours before droplets spontaneously form.
In above-freezing temperatures, the air would have to be supersaturated to around 400% before the droplets could form.
Last Updated on 18 hours by pinc